Modern telecommunication systems require that the communication lines and trunks connecting a central office system to subscriber stations and other offices be maintained at a high performance level. It is necessary, therefore, to provide means to accurately measure transmission characteristics of the communication lines and trunks with minimum service interruption. Specifically, in toll offices which have extensive trunk interconnections with other telephone offices, trunk test circuits must be provided which effectuate accurate and convenient measurement of losses and noise levels associated with signal transmission in each direction on the trunks. Often, a modern toll office will have automated trunk test apparatus which requires sophisticated equipment at the remote office. For a small remote office having a small number of interoffice trunk connections, on-premises test equipment necessary to utilize modern automated test apparatus at a connected toll office may be prohibitively expensive.
Customarily, for the small remote office, trunk test functions are accomplished via manual procedures at a testboard terminal within the remote office and partially automated circuits. The prior art describes two alternatives for the toll office, when manual trunk testing is required at the remote office. The first alternative is to provide manual testboard-to-testboard testing functions, thereby necessitating a craftsperson at the toll office testboard terminal. Such manual testing fails to take advantage of the sophisticated electronic equipment generally available in a modern toll office. The second alternative is to provide an automated trunk test circuit at the toll office which is compatible with manual testboard procedures at the remote office. A prior art arrangement in accordance with the second alternative is described in U.S. Pat. No. 2,721,235, B. McKim et al. However, the circuit arrangement described in the McKim et al. patent utilizes high impedance vacuum tubes and electromechanical devices which are incompatible with the speed of execution of associated circuitry in a modern telephone office. Further, the prior art arrangements generally do not provide the precision required for accurately measuring transmission characteristics of trunk circuitry of modern electric telephone offices.